Wan Hongyi, Islam Mohammad Saiful, Qian Dali, Ormsbee Lindell, Bhattacharyya Dibakar
Department of Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky 40506-0046.
Electron Microscopy Center, College of Engineering, University of Kentucky, Lexington, Kentucky 40506-0046.
Chem Eng J. 2020 Aug 15;394. doi: 10.1016/j.cej.2020.125013. Epub 2020 Apr 8.
In this study a systematic comparison in morphology, long-term degradation, regeneration and reuse were conducted between palladized and sulfidized nanoscale zero-valent iron (Pd-Fe and S-Fe). Pd-Fe and S-Fe were prepared, after the synthesis of precursor Fe nanoparticles (spherical, ~35 nm radius) for carbon tetrachloride (CTC) treatment. With HAADF-TEM-EDS characterization, dispersive Pd islets were found on the Fe core of Pd-Fe. However, the Fe core was covered by the FeS shell of S-Fe (FeS/FeS = 0.47). With an excessive Pd dose (10 mol%), the Pd-Fe were dramatically deformed to dendritic structures which significantly decreased reactivity. For CTC degradation, Pd-Fe (0.3 atomic% Pd) increased the degradation rate by 20-fold (k= 0.580 Lmmin) while S-Fe presented a greater life time. The major intermediate chloroform (CF) was further degraded and less than 5% CF was observed after 24 h using Pd-Fe or S-Fe while above 50% CF remained using Fe. During aging, the Fe core was converted to FeOOH and FeO/γ-FeO. The restoration of Fe was achieved using NaBH, which regenerated Fe and Pd-Fe. However, the formed FeS shell on S-Fe was disappeared. The results suggest that S-Fe extends longevity of Fe, but the loss of FeS after aging makes S-Fe eventually perform like Fe in terms of CTC degradation.
在本研究中，对负载钯和硫化的纳米级零价铁（Pd-Fe和S-Fe）在形态、长期降解、再生和再利用方面进行了系统比较。在合成用于四氯化碳（CTC）处理的前驱体铁纳米颗粒（球形，半径约35nm）之后，制备了Pd-Fe和S-Fe。通过高角度环形暗场扫描透射电子显微镜-能谱（HAADF-TEM-EDS）表征发现，在Pd-Fe的铁核上存在分散的钯小岛。然而，S-Fe的铁核被FeS壳层覆盖（FeS/FeS = 0.47）。当钯剂量过高（10mol%）时，Pd-Fe会显著变形为树枝状结构，这显著降低了反应活性。对于CTC降解，Pd-Fe（0.3原子%钯）使降解速率提高了20倍（k = 0.580 L/(mmol·min)），而S-Fe具有更长的使用寿命。主要中间产物氯仿（CF）进一步降解，使用Pd-Fe或S-Fe时，24小时后观察到CF含量低于5%，而使用铁时CF含量仍高于50%。在老化过程中，铁核转化为FeOOH和FeO/γ-FeO。使用硼氢化钠实现了铁的还原，其使铁和Pd-Fe得以再生。然而，S-Fe上形成的FeS壳层消失了。结果表明，S-Fe延长了铁的寿命，但老化后FeS的损失使得S-Fe在CTC降解方面最终表现得与铁相似。
